1. Field of the Invention
This invention relates to a multi-directional, light-weight, high-strength interlaced material and method of making the material, and more particularly to a multi-directional, light-weight, high strength interlaced material suitable for use in or for structural members in military and commercial aerospace and aircraft applications, as well as other commercial applications.
2. Description of the Prior Art
In the past, high-strength structural members in military and commercial aerospace and aircraft applications, as well as other commercial applications, have normally been constructed of various types of metals. In recent years, there has been a trend toward the use of fiber-reinforced plastic composite materials for this purpose, because of their various advantages. For example, when compared to traditional structural metals such as steel, aluminum and titanium, fiber-reinforced plastic composites are lighter, easier to use, stronger, less expensive, less subject to corrosion and more impact resistant. By way of illustration, carbon fiber material impregnated with thermoplastic may be five times stronger than steel and 55% lighter than aluminum.
In general, fiber-reinforced plastic composites are formed by arranging continuous, light-weight, high-strength fibers, such as carbon, glass, boron, various high strength metals or various synthetic fibers, such as aromatic polyamides, and lesser strength fibers such as rayon or nylon, in side-by-side bundles or tows with the fibers extending longitudinally in one direction. The side-by-side fiber bundles or tows then are impregnated with a plastic matrix under simultaneous heat and pressure. Subsequently, the resultant fiber-reinforced plastic composite may be arranged in layers in sheet, or unidirectional tape, form which, when subjected to heat and pressure, form a fiber-reinforced plastic composite laminate.
Fiber-reinforced plastic composites are available in fiber-reinforced thermoset matrices or fiber-reinforced thermoplastics matrices. Fiber-reinforced thermosets are epoxy, vinylester or polyester-based, harden through an irreversible catalytic process and require a long curing cycle as part of the process through which they are fabricated into finished parts. Prior to use, fiber reinforced thermosets have delicate shelf-life properties and require refrigeration. When cured, fiber-thermosets are strong and light-weight, but often brittle.
Fiber-reinforced thermoplastics, on the other hand, are a newer form of composite which, compared to fiber reinforced thermosets, have significantly higher toughness and impact resistance, are processed at and can tolerate higher temperatures and have improved moisture and chemical resistance. Fiber-reinforced thermoplastics do not require refrigeration, have an unlimited shelf life and require only a short heat/cool cycle for curing. Unlike fiber-reinforced thermosets, fiber reinforced thermoplastics are not hardened through a catalytic process and therefore can be reheated and reformed without undue detrimental effect, although they do require higher temperatures than fiber-reinforced thermosets to process them into finished parts. Further, fiber-reinforced thermoplastics tend to be stiff and boardy, and therefore generally are unable to conform to highly contoured molds at room temperature.
Fiber-reinforced thermoset composite unidirectional tapes have been used extensively for high strength structural aerospace/aircraft applications because all fibers, and therefore all the structural attributes of the material, are aligned in one direction. (To date, however, the processing of these tapes into finished parts has been too expensive for most commercial applications.) Unidirectional tapes are laid in successive laminated layers at predetermined angles, to obtain the desired structural properties in a finished format of greater dimensions than the individual tapes. An example of such laminated fabrication is shown in U.S. Pat. No. 3,946,127, to J. R. Eisenmann et. al. Normally, the unidirectional tapes are processed by hand; however, for some larger parts, complex automated tape laying machines, having a cost on the order of one to three million dollars, may be used, although such machines for processing fiber-reinforced thermoplastic composite unidirectional tapes are still in the development stages.
Fabrication of parts from fiber-reinforced thermoplastic composite unidirectional tapes has followed the labor-intensive processes developed for fiber-reinforced thermoset composite unidirectional tapes. Fiber-reinforced thermoset tapes, however, are more suitable for these hand processes because, unlike fiber-reinforced thermoplastic tapes, they can be fabricated so that they remain tacky until cured and thus can be more easily held in position, whereas hand lay-up of fiber-reinforced thermoplastic tapes requires that each tape be tacked, welded or stitched in position before laying the next tape.
Thus, a particular need exists for a light-weight and high-strength fiber-reinforced composite material which covers large areas economically without loss of the structural characteristics of unidirectional tapes and which can be fabricated automatically in a rapid, efficient and inexpensive manner.
Accordingly, a primary purpose of this invention is to provide a new and improved multi-directional, light-weight and high-strength fiber reinforced plastic composite material of this type, wherein the unidirectional fiber-reinforced plastic tapes initially are interlaced in over-and-under relationship in a 0 degree/90 degree configuration. The interlaced material, which may be fabricated automatically in a machine known as a composite material interlacer, subsequently is subjected to heat and pressure in single or multiple layers to form an integral structure.
In general, the weaving or braiding of yarns, strips or ribbons of material in the forming of various types of parts is known in the art. For example, U.S. Pat. No. 2,162,598 to H. N. Atwood discloses the forming of a composite shatterproof window glass in which glass strips or ribbons are passed through or immersed in a molten plastic bath, subsequently braided, woven or interwoven into a fabric, and then subjected to heat and pressure to unite and bond the plastic-coated strips together. Similarly, U.S. Pat. No. 3,439,685 to M. I. Port et. al. discloses the weaving of flat plastic yarn and passing the woven yarn through heat rolls to bond the yarns slightly to prevent slippage therebetween.
U.S. Pat. No. 3,974,313 to V. L. James discloses an energy absorbing blanket comprising layers of cloth woven from tapes formed from glass filaments, an aromatic polyamide or other materials, in various patterns, so that the tapes of the layers can move relative to one another to absorb energy, e.g., of a projectile. U.S. Pat. No. 4,030,892 to L. I. Mendelsohn et. al. is directed to an electro-magnetic shield which may be woven from filaments including a glass metal alloy. U.S. Pat. No. 3,769,144 to J. Economy discloses a central layer of woven carbon cloth disposed between two outer reinforcing layers to form a quilted fabric for use in fabricating gas-impermeable protective clothing or gas masks. U.S. Pat. No. 4,412,854 to G. K. Layden concerns a method of producing a fiber-reinforced material by painting a thermoplastic polymeric binder, containing glass powder, on woven carbon cloth, drying the resultant sheet, cutting the sheet to produce a plurality of preforms of a desired shape, stacking the preforms in a mold, initially warm-molding the preform to form an intermediate article, and then hot pressing the intermediate article to form a final article.
It also is known to form tape yarns on a circular loom into a tubular member which may be used in that configuration, or may be cut longitudinally to form a sheet of planar material. For example, circular looms of this general type are shown in U.S. Pat. No. 2,454,146 to G. E. Ezbelent, U.S. Pat. No. 3,719,210 to P. D. Emerson et. al. and U.S. Pat. No. 3,871,413, to S. Torii.
Heretofore, however, the prior art has not provided a multi-directional, light-weight, high-strength fiber-reinforced plastic composite material which can be fabricated in a rapid, efficient and inexpensive manner, and which can be used for forming parts of tubular, planar or contoured configuration, and a primary purpose of this invention is to provide such a material and a method of making the material.